<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<h1 id="message">Hello, world!</h1>
		<button id="btn">0</button>
		<script>
			var counter = 0;
			var btn = document.getElementById('btn');
			var h1 = document.getElementById('message');
			function f1() {
				alert('按钮被点击了!');
				if (btn.removeEventListener) {
					btn.removeEventListener('click', f1);
				} else {
					btn.detachEvent('onclick', f1);
				}
			}
			function f2() {
				counter += 1;
				btn.textContent = counter;
			}
			function f3() {
				h1.textContent = 'Goodbye, world!';
			}
			if (btn.addEventListener) {
				btn.addEventListener('click', f1);
				btn.addEventListener('click', f2);
				btn.addEventListener('click', f3);
			} else {
				// 低版本IE浏览器
				btn.attachEvent('onclick', f1);
				btn.attachEvent('onclick', f2);
				btn.attachEvent('onclick', f3);
			}
		</script>
	</body>
</html>
